International resistance testing guidelines updated

The International AIDS Society has updated its guidelines on resistance testing in HIV infection, first published at the beginning of 1999.

The only substantive difference with British HIV Association anti-retroviral treatment guidelines is the British recommendation that resistance testing should be carried out in all chronically affected patients prior to starting treatment.

IAS recommendations:

• Consider resistance testing before starting treatment in areas where primary drug resistance is appreciable
• Primary infection: all patients presenting with symptomatic primary HIV infection should be tested before commencing treatment, and also for surveillance purposes
• First regimen failure: exclude poor adherence or PK problems, and obtain blood for resistance testing before stopping or changing the failing regimen. Resistance testing may not be necessary if the clinician is confident about the patient's treatment history and when the therapy switch occurs soon after treatment failure is identified whilst viral load is low [level not specified]
• Resistance testing is likely to helpful (after excluding poor adherence or PK problems) where:

1. A suboptimal response to first line treatment has occurred despite good adherence
2. Viral breakthrough after an initially good response to therapy
3. Viral rebound has been prolonged, thus permitting the accumulation of multiple resistance mutations